Mechanisms underlying coal instability during coal and gas outbursts induced by deep mining
摘要
Objective The gradual depletion of shallow coal resources drives a shift to the mining of deep coal seams. However, the complex deep mining environment significantly increases the potential risks and severity of coal and gas outbursts. Therefore, there exists an urgent need to investigate the mechanisms underlying the mechanical instability of coals under deep mining, aiming to provide guidance for the safe mining of deep coal mines.Methods By integrating physical experiments, numerical simulations, and theoretical analysis, this study investigated coal and gas outbursts under burial depths of 500 m, 1000 m, and 1600 m and established a multi-field coupling model that incorporates the coal deformation, gas flow, and coal damage fields. Furthermore, it revealed the mechanisms underlying the mechanical instability of coals during coal and gas outbursts under deep mining.Results and Conclusions Physical experiment results indicate that during coal and gas outbursts, the coal seams exhibited a rise in the pressure relief rate as the burial depth increased, with the relative outburst intensity increasing to 29.05%, 38.05%, and 42.70% under burial depths of 500 m, 1000 m, and 1600 m, respectively. The post-outburst temperature of the coal seams was found to decrease significantly as the burial depth increased, with the maximum temperature drops reaching 0.17 ℃, 0.37 ℃, and 0.55 ℃ under burial depths of 500 m,1000 m, and 1600 m, respectively. During coal and gas outbursts, the migration velocity of pulverized coals was observed to increase with the burial depth, reaching peaks of up to 22.08 m/s, 22.87 m/s, and 26.58 m/s under burial depths of 500 m, 1000 m, and 1600 m, respectively. Overall, a greater burial depth corresponded to a stronger outburst dynamic. Numerical simulation results reveal that with decreasing lateral pressure coefficient and increasing gas pressure during coal and gas outbursts, the coal damage zone evolved from a semicircular shape to a butterfly sh